The attorneys filed a civil suit arguing that special counsel Robert Mueller's investigation had overstepped its bounds.

Attorneys for Paul Manafort, the former Trump campaign chairman facing charges born of special counsel Robert Mueller's Russia investigation, had their civil case picked apart and shot down by a federal judge Wednesday.

Manafort's lawyers argued that Mueller's investigation had overstepped its bounds.

“I don’t really understand what is left of your case,” U.S. District Court Judge Amy Berman Jackson said to Kevin Downing, Manafort’s attorney, after peppering him with a lengthy series of questions.

Manafort filed a civil lawsuit on Jan. 3 against Mueller and Deputy Attorney General Rod Rosenstein, the Justice Department official who appointed the special counsel, in a key legal test of how far Mueller’s mandate extends.

None of the charges against Manafort are related to his work with the Trump campaign, but include conspiring to launder money, failing to register as a foreign agent, bank fraud and filing false tax returns.

He has pleaded not guilty to all of the charges.

Manafort’s civil lawsuit relies on an arcane law called the Administrative Procedure Act, which spells out the process federal agencies must follow when writing regulations. It alleges portions of Rosenstein’s order laying out Mueller’s investigative mandate violate Justice Department rules.